Brake actuator service chambers of the type disclosed herein are used on trucks, semitrailers, buses and other large vehicles to actuate the braking system of the vehicle. The service chamber includes a metal housing defining a chamber therein having an end wall which is mounted on a bracket on the vehicle having an opening therethrough which receives a reciprocal pushrod supported in the service chamber. The pushrod has an end portion extending through the opening in the end wall of the housing. The service chamber generally includes a cup-shaped flexible diaphragm secured at is periphery in the service chamber and one end of the pushrod includes a generally flat piston which is received against the flexible diaphragm. Upon actuation of the braking system of the vehicle, pneumatic pressure acts against the side of the flexible diaphragm opposite the pushrod piston, driving the piston through the housing end wall and actuating the vehicle brakes. The brake actuator service chamber may be mounted in tandem with a spring or an emergency chamber or the service chamber may be used alone or in combination with a separate spring chamber.
The service chamber alone or in tandem with a spring chamber is mounted on a bracket attached to the vehicle. The end wall of the service chamber generally includes a pair of holes on opposed sides of the central opening which receives the reciprocal pushrod and bolts are mounted in the holes which attach the service chamber to the vehicle bracket. The mounting bolts may, however, be welded or otherwise attached to the end wall of the service chamber.
As will be understood by those skilled in the art, brake actuator service chambers are exposed to dirt, debris, mud, ice, sleet, etc. which may interfere with the operation of the service chamber or result in wear or deterioration of the components of the service chamber. The service chamber, for example, includes a return spring which is generally biased between the end wall of the service chamber and the piston head of the pushrod. Thus, for example, dirt or ice may interfere with operation of the return spring, which returns the pushrod to its ready position, or cause deterioration of the flexible diaphragm, which is generally formed of synthetic rubber or Neoprene.RTM.. The prior art does include annular stone shields mounted in the service chamber surrounding the reciprocal pushrod and tubular flexible dust boots mounted on the pushrod. However, the prior art does not disclose an adequate and practical seal which seals the pushrod opening in the end wall of the service chamber. This is due in part to the fact that the pushrod does not always move directly in a straight line. Instead, the movement of the pushrod is sometimes skewed from the central axis of the brake rod. Thus, the prior seals have had difficulty in maintaining a seal under the extreme conditions of a brake actuator service chamber. Thus, it would be desirable to have a seal for the pushrod opening in the end wall of a brake actuator which can survive in the actual environment in which the brake actuator is used and which will provide a good seal under the operative conditions faced by the brake actuator.
Finally, it would be most desirable to more firmly mount a service chamber on the vehicle mounting bracket to reduce damage from the vibration encountered by such vehicles. Most brake actuator manufacturers subject their brake actuators to vibration testing; however, such testing is done under ideal conditions. In actual practice, the brake actuator is subject to vibration under severe conditions which may result in damage to the housing or components of the brake actuator. This is particularly true with "piggyback" brake actuators wherein the spring chamber is mounted in tandem with the service chamber because of the additional loads.